Force and Pressure

What is a Force?

A push of pull

What are the effects of forces?

Change the speed of a moving object,
either by increasing its speed or slowing it
down

Change the shape of an
object or size of an object

Change the direction of a moving object

Start an object moving or
stop a moving object

you cannot see a force but you
can see the effects of forces.

How can we measure a force?

Using a force-meter

Spring-balances, Extension spring balance, Spring stretches when a force pulls on it, Compression spring balance, Spring is compressed when
a force acts on it

SI Unit: Newton(N)

What are the important forces around us?

Frictional Force

Occurs whenever there are
two moving surfaces in
contact

Slows down and stops a moving object

Produces heat

Friction can be useful, Friction holds a nail in the wall, Friction between the wheel and
the brakes slow down the
bicycle, Friction between our feet and the
ground gives us the grip needed to
walk and run

Friction can be a problem, Makes movement more difficult, Wears away materials

Magnetic Force

Magnets can attract objects
made of iron and steel

Magnets exert a force called
magnetic force

Examples of Magnetic Force, Magnetic catch for the door of
a cabinet keeps the door shut, The needle of a compass is a small
magnet. A compass is used to give
directions, A magnet attracts steel pin. Picking up
the pins ourselves may injure our
fingers, A crane uses a powerful
magnet to lift iron and steel
objects

Forces between magnets, Magnets can exert a force on other magnets, Bar magnets each have a
North and South pole, Like poles repel (Push), Unlike poles attract (Pull)

Gravitational Force

A force that pulls objects
towards the Earth

Exists between any two objects

Weight

Weight of an object depends
on the force of gravity
pulling on that object

The greater the force of
gravity pulling on an
object, the heavier the
object

What is Pressure?

The amount of area applied
onto an object

Pressure depends on 2
things: 1) Force 2)
Area

The pressure increases when
the force increases, while
the area decreases

Increasing Pressure by reducing Area

For the same force, when a
smaller surface is in
contact with an object, the
pressure exerted on the
object is higher

Reducing Pressure by increasing Area

Low pressures are needed
when people or machines
move on soft ground or
snow

When a larger surface is in
contact with the ground,
the pressure exerted on
the ground is lower, so
people and machines can
move without sinking